Fast nailed it, needs a wider spread at altitude to enhance the high RPM pumping efficiency.

Small ports (for a given displacement) can actually be advantageous at altitude in helping keep the VE up. Compared to atmospheric pressure it will take longer for the motor to 'run out of port' since less air is metered per RPM.

Your bigger ports are acting comparatively 'lazy' at lower piston speeds at high altitude....and once you gains mention the narrow cam (which would still work well at sea level if you have good CFM capacity) reduces the VE at the point where the ports can start really working.

A wider separation phased later would help the top end more than it would hurt the bottom/middle