So as I RTFM . . . If you AC-couple you get up to 90A of cruft from the micro-inverters + another 50A from the PV. The only limitation is PV->grid which is 50A (12KW). Thus assuming you have a beast set of micro-inverters, and direct PV coming out your behind, with a single 18kpv you can push 30+KW back towards the grid lugs/panel. Assuming you've properly configured your export settings and installed the CT's properly you should be golden.
I'm not sure where the problem is, perhaps there is a mis-communication as the thread gets deep. Put the Enphase stuff on the gen lugs, turn on AC coupling. You have access to all the power, sans any direct PV over 12K, which can go to the batteries I think. Do you actually have > 12KW of direct panel output on a single unit?
At some point you have to buy more hardware and/or re-engineer, and frankly I would never run my stuff constantly at the edge of it's capability. YMMV. My 32 panel array of 4x8x455w has hit over 12, theoretically it's a little under 15, but I have it split between two. I mean if you want to mix 20 different types of solar equipment more power to you but you seemed to indicate you have ~18K of micro-inverter stuff, which should work in cahoots with the 18kpv as documented in the manual. If you are trying to get creative and use it in an undocumented manner, that is generally unwise.
From the manual:
View attachment 205165