There is no mention of throttle position during engine prime in the POH, nor was it mentioned during my TacAero training week, and in talking with other FX-3 owners, they've been doing the same thing as me, priming with the throttle all the way back or 1/2" from back/closed (start position). I enjoy watching YouTube videos of various flying and came across a Cirrus SR-22 video (normal aspirated) and noticed during his engine start he put the throttle to full open prior to doing the prime. The cluebird landed for me, duh, you need to open the throttle to allow the prime to flow, i.e. increased fuel flow position. I've had problems with starts such as priming 5 seconds, won't start, prime some more, eventually starts. i.e. multiple cranks to get a start.
I tried the procedure of prior to engaging the fuel pump to put the throttle full open. My starts are fast now and never need a second turn of the key. I verified this situation with Pete at CC. Others have tried it as well after I mentioned it also with success. I would recommend the POH "template" be updated in section 4.3.2.2 to offer a throttle position in the engine start procedure prior to prime then prior to starter engage.