AFR slowly richens at idle

Dont want to create new thread so I will try to get some help here.
My spec is similar in a way:
470ci 11:1, 4.10 rear, 29” tire, mvb 727, cam 260/[email protected], .700 net lift solid roller with 108lsa. Max wedge port heads, 1050 dominator. Timing is 34 degrees locked. Vacuum at cruise is 12, at idle in gear 6, idle in park around 10. Normally I like to have lean idle and lean cruise, but my setup gives me hard time getting there. Also time of the year is problematic because it’s cold out and cold starts cause fouled plugs so I can’t really use them as mixture indicator. I drive too short distances for plugs to clean up so I need to rely on afr gauge. This cam has around 45 degrees overlap so I assume afr reading is a bit off meaning it shows leaner than it really is? Yet it idles best at 13.2-13.4in Park and 14.0-14.2 in gear at 1250ish in Park and 950ish in gear.
I prefer to have it lean at 15 in gear but then my vacuum drops to 5 max and I need to have almost 1400rpm in park to maintain around 900rpm in gear. I have no problem crusing at around 15afr with these settings.
Should I just leave it as is till I can actually drive the thing of perhaps some air bleeds tuning is an option for me?

Can too tight converter be an issue here? I plan to change it before summer, it stalls around 3300, wanted to go to 3800+

With smaller cam lean idle was not an issue.