To the question if market cap is a good proxy for EVIC, that naturally depends on the financial structure of the specific company. For a company with low financial leverage and will little cash on the balance sheet, it may be, but the higher up you get in terms of financial leverage and cash levels, the less appropriate it becomes.
The volatility of market cap (and EV) is also making any market valuation-based denominators less useful in SBTi’s view, as any progress in the metric can be influenced by movements in market valuations. Rising valuation means that a company/portfolio may seem to be making greater improvements compared to its history than what it really is in terms of absolute emissions reductions in the real economy.
Therefore, SBTi favors the much less volatile passive side of the balance sheet and total assets as the denominator or alternatively use revenue, again for its more stable properties for most companies and portfolios.