ISKY Retainer Question, 507ST and 507STA 7 Deg Locks

Not sure if this is the right place to ask, but I figured SBM engine builders might know an answer.
I was on the phone with ISKY yesterday and we determined the 507 retainers are right for my springs.
What they could not answer was "What is the difference in an ST and and STA?"
The STA is, in their database, a +.060 retainer.
They did measure one on it's side and the difference is this.
An ST measures .390 and a STA measures .440, retainer top to retainer bottom.
Trying to wrap my head around what that really means.
I can't take moving the valve tip any lower into the retainer.
But if it decreases the installed spring height that would explain the +.060 number.
Any ideas?
I guess they don't publish, or have, detailed data to keep their competitors from building the same part.