Z2 metabolism Q

TLDR:
Did a substrate/VT lab test. Highest fat usage occurs in my Z1 not Z2, as described in TFUA.

I did a substrate lab test today which gave me the numbers for my zones (VT1/2 occurs just before LT1/2).

From the substrate testing, my fat max is in my Z1 but on the https://uphillathlete.com/aerobic-training/uphill-athlete-training-zones-heart-rate-calculator/ it mentions that Z2 is where max fat utilisation occurs

My top of Z2 is 50:50 fat:carb usage with bottom of Z2 62:38 fat to carb. Mid Z1 is 87:13 fat to carb.

Do I take FATMAX as top of Z2 or the VT1 as top of Z2? I have read that a longer test should perhaps have been done and I'll do that next time (tester is on board with it).

Appreciative of any input 🙏🏼