The reclasses are "notchy" if that makes any sense. Meaning the only way to do a reclass to keep the SM in PTE (after suspension and other points are added) are the ones they published. If you had a higher HP car you would end up with a * (PTE +7 base) and none of the cars on SM tires could stay in PTE anyway. The miatas due to their top notch chassis are handicaped vs other cars admittedly and FWD cars in general get way more WHP allowance than RWD cars due to the adj factors.
In most cases nowadays one is better off using a reclass. I believe from anecdotal evidence that the reclasses have become more favorable as of late. I think they are trying to encourage people to reclass and reclass often in PT/TT.
I wont go into my long winded personal opinion but i would do it differently were i running PT, but, i'm not....
I think the case is being made here through all this is: It is indeed not within the PT rules and not fair to just pull a restrictor on a SM and be a PTE car (+6 for head work or not). Do all the available spec miata mods make sense as "mods" in PT (like the chin spoiler), of course not. BUT the whole idea of the NASA TT/PT system is open modification allowances accounted for by points, applied in a threshold manner, giving people enormous flexibility in building a car, while trying to keep the rules under 25 pages or whatever...PT wasn't written so spec miata's could sweep E3 Enduro Podiums. Does this mean the SM is the ideal PTE car? again, nope...
The head issue in my mind is semantics. It's going to end up being a dyno thing anyway....so most likely 94-05 cars would be best off with pulling the spoiler when they pull the plate and running it that way hoping they don't go over the 138 on a dynojet. (assuming that math is correct).
Now if specific NASA regions are not interested in all these messy details, so be it. In my region i'm simply trying to enforce the rules as written, universally, to encourage good competition and NASA credibility.