Car financing 20% rule question

Is the 20% of your income rule based on Gross or Net income?

I'm thinking of taking the dive for a Tesla Model X and currently gross about $170k per year for myself, not including partner income. No kids, and no plans to have any (not biologically possible anyway so no accidents =D ), 12k credit card debt, which should be paid off by Nov. $2760 PITI house mortgage payments.

No other real source of debt besides current $364 auto lease payment on a 2016 Kia SoulEV that I will be trading in and $199 lease on a Honda FitEV we keep as a second car. The incentives on the car were actually really good and it has equity as of right now.

If based on Gross, I calculated a $2800 / mo max payment @ 20% which basically is more than any Tesla costs. Net is more like 1600 max payment because of all my 401k and ira contributions.

I really just want a maxed out X90D sans options I know I will not need or never use, which is just the quicker charge rate for home charging. $114250 cash price without any rebates. $1488/mo finance rate. 825 credit score so I will definitely qualify for the 1.49apr

I've been keeping my eyes peeled for an inventory/showroom model that has >2000 miles to get the 10-15k discount, but none have had all the options I wanted.