Welding Tips and Tricks

This was my first time welding with Inconel filler for TIG. I have SA387 GR22 (2 1/4 chrome) welded to 304H.
There isn't much of a WPS other than what the inspectors want me to create. My preheat has to maintain 300+ F during welding. I have 1" thick 18"x6" double bevel plate test. I used no gap with a 40-60 degree bevel. Allowed to back gouge.
The comments for setting this up were- ERNICR-3 Root and Fill. Inco 82/182 Tig/Stick. 309l for buttering

I am having a hard time getting the first root pass not to crack. I had to cut out the root pass twice on one side and once on the other. I don't feel confident about it, But I have already finished the coupon... I heard a tang like crack.
Also, I feel there is something I am missing on the Inconel wire; Such as, what is the right amount to add per inch? Should I add more or same amount in comparison to stainless?
Anything else to add about Inconel filler that I am missing?

Try a small gap. You may be getting a lot of stress from shrinkage. I've done very little with that material but I've been told you need to keep welding till you have almost an 1/8 or more of weld thickness till cracking isn't an issue.