I would be more inclined to follow Georges tuning procedure here to get a better result with the current measurement that you have from the spl meter especially with respect to altering the target decay

https://www.meridianunplugged.com/wiki/index.php?title=MRC_Tuning

this can give you a range of optional correction filters to choose from , you could even get a better result by experimenting with tweaking the filters manually.

Rgds
Stuart

Linn LP12, Ittok LV11, Arkiv, Linn Kairn as a phono stage, MPmax 221, DSP6000's, WiiM Pro streamer.