You're not remembering it wrong.
The only year in Detroit Verlander pitched as well as he has in Houston was his Cy year in 2011, with a 0.92 WHIP, 2.40 ERA and 24 wins.
He HAD improved his pitching in Detroit in 2017 prior to being traded at the end of August... but wasn't pitching well enough at the trade deadline to get traded. In 6 August games though, 4-1, 2.36 ERA, 0.79 WHIP... Electric! He did do better in Houston though, in 5 games at 1.06 ERA and 0.65 WHIP, phenomenal!
The scuttle was that Houston had improved the spin on one or two of his pitches... I don't remember, but it was something like that. But... the small sample sizes in both August & September are just too - small - to really draw any conclusions.
However, in his 98 games with Houston, ages 34-39, 2.30 ERA, 0.84 WHIP, 2.96 FIP.
With Detroit, from ages 22-34, in 380 games, 3.49 ERA, 1.19 WHIP, 3.48 FIP.
Again, the only year JV had with Detroit that was as good as his pitching in Houston, was his Cy year in 2011.
Now... he's pitched a whole lot less in Houston, annual innings-wise... but I'm thinking Houston helped him tweak a pitch or two and he's been a bit more effective there... in his lesser innings that is...