Seeing reduced consumption since using Coastal "Syn" as make-up oil

[Islandvic]

I few k miles ago, I serviced my '96 Vic with a MoCraft filter and M1 5-30. It consumed oil at a higher rate with the M1 than with the ValMaxLife Syn I was using. 600miles/qt vs 1000miles/qt. As make up oil, I have used 2 qts Castrol SynBlend 5-20 and my last make up quart was Coastal Synthetic API SL 10-30 (AZ $0.99/qt sale). That was 900 miles ago and consumption has decreased. I added another qt of the Coastal "Syn" yesterday. Is there a coorelation between decreased consumption and the Coastal "Syn", or is my 4.6 getting used to the M1? Thanks