Evaluating Validity of High VTC in TikTok Campaigns for Accurate ROAS

We are currently analyzing TikTok campaigns where 90% of conversions are attributed to View-Through Conversions (VTC). Out of 30,000 total conversions, 27,000 are VTC and the remaining 3,000 are Click-Through Conversions (CTC). This disproportionately high number of VTC makes our Return on Ad Spend (ROAS) seem overly inflated, raising concerns about its accuracy. While it is possible that users viewed our ads and later converted, we lack concrete evidence that the ad directly influenced these conversions. Alternatively, for our YouTube ads, we observed a 60% CTC and 40% VTC split, allowing us to confidently use these percentages to calculate conversions. Applying a similar method to TikTok by using 90% VTC still results in unrealistically high conversions. We are seeking a data-backed approach to determine a reliable percentage (X%) of VTC, rather than an arbitrary figure. Is there a way to derive this percentage using other TikTok metrics? Any advice on generating believable conversions and ROAS for these TikTok campaigns would be greatly appreciated.