Nosecone coupler length

I will be flying my Avalanche on 38mm motors as a single deploy with a chute release. As such there will be no head end deploy, however I will be using a Atteberry Head End Altimeter Bay for a BRB900 and a Alt3. The nosecone coupler has 4 1/4" exposed. I am wondering if I might shorten that to give more room in the body tube. However I am unsure how much coupler is needed to extend into the BT. How much dare I take off? Is there a rule of thumb? Ideas?

The rule of thumb for coupler length is one body diameter.

Thank you Buckeye!