""there was no symptom of a lean condition while driving it. Only when it was sitting in park. Why is that?""

When you are sitting in P at high idle, you are idling on the transition circuit. When you are tooling around town, you have help from the front pump circuit to help on acceleration until your mains start in. The pump circuit is a designed-in "bandaid" to help cover up any lean spikes during the transition into the mains. It sounds like your current pump setup (squirters/pump cam) is doing its job along with the .028/64 main setup.

Since you are using 64 jets and .028" MAB's (fairly rich which starts the main circuit sooner than a .033" for reference), this may be allowing the main circuit (jets and MAB's) to start fairly early and the main circuit may be tuned fine. This might be why you do not have any known issues while cruising.
Please concentrate on richening the IFR's and the IAB's.