If you don't believe the geometry changes,then how about rocker arm ratio?

Mr P, You are right it doesn't change the relationship of the valve tip to the rocker;But if the adjuster ball is closer to the rocker,lift will increace.

1.25 - 1.5 sounds good to me. Check oiling with a drill motor and turning the crank. If OK you are ready to go.

technically speaking, adding lash caps does change the geometry. it doesn't change the fulcrum point, but it does change the sweep of the rocker tip over the valve tip. also, moving the adjuster farther or closer to the fulcrum to change the ratio, also changes the geometry since the force applied from the pushrod needs to be greater since it is closer to the fulcrum on that side.
think of a teeter totter for a reference. it's all basic geometry. now replace the kid at either end with a valve tip and a rocker adjuster at either end. any time you change the position of any of the three pieces, your changing the "geometry", regardless of how much and regardless of the effect.

LOL, You guys would argue over the color of a black board.
I dont understand why were talking and even arguing about stuff that is irrelevant, doesnt matter and cant change LOL
-Push rod length doesnt effect geometry
-how much adjuster is hanging out doesnt affect geometry
How far the adjuster is located from the cup does change the ratio, how else would one change it?
It cant be changed unless you buy another rocker arm so why bring it up?
also with little to no thread protruding from the rocker arm can cause problems with push rod interference where the cup actually contacts the rocker body.
This isnt a problem with cup adjusters and ball end/ball end push rods...
I have no proof or hard evidence but I truly believe that cup adjusters and ball end/ball end push rods are better than cup style push rods from burning up etc. But thats another story and doesnt matter here either.
Lash caps will effect geometry a little. I have used lash caps on diff projects and engines over the years maybe a half dozen times. To be honest I it has really never made any significant changes either way.
Some engine builders avoid lash caps like a plague, but why?
I think they definitely serve a purpose, and in some cases save the engine builder a bunch of money.
i have heard horror stories about guys trashing engine or loosing lash caps, but IMO thats not the lash caps fault. If the lash cap is to deep and it pushes against the valve lock, its not the lash caps fault.
Bottom line if these are Isky, or Crane type Ductile type rockers anything from 1 to 3 threads showing will be just fine....
IMO 1 /2 thread is pretty idea...

Oh , No doubt, the geometry is changed by both the adjuster length and a lash cap. The lash cap has a lessor effect,IMO over the adjuster length. Combined they can have a greater effect.

In the scheme of things though I wouldnt use it as a tuning device, Id be more concerned with the best valvetrain strength of the geometry aspects. Shortest adjuster length and best roller sweep over the valves tip. mike

I'd like to make a clear distinction in terms.
"irrelevant" (meaning, nothing to do with it) isn't true, all those dimensions affect geometry, lift, wear etc. - the question is in what way, and how much?

"doesn't matter" is actually true in many cases, you get an error but the effect is very small, or 2 errors almost cancel each other out. Sometimes an accidental change corrects an unseen error.

"Push rod length doesnt effect geometry": well, not directly (a fixed length hydraulic pushrod is always "right"), but will if you need more adjuster to make it up.

"how much adjuster is hanging out doesnt affect geometry": it not only changes the ratio (more threads = lower ratio), it changes the angle between the 2 rocker levers (pushrod side and valve side), which is part of the basic rocker design. The rocker's inter-lever angle is the total of the pushrod angle (not the tappet bank angle) and the valve stem angle (15°, 18°, etc.). If the pushrod is 0° (parallel to the cylinder) the angle is just the stem axis. If the lever total changes (as with too many threads), the arc of either the pushrod side, the valve side, or both cannot be centered, and the sweep and scrub increase.

Yes, it's a complicated subject.