158e On Cover Maybe?

I'm not new here but haven't posted for a while. I bought a green Washington on cover figuring it was a 136 or 136a. After receiving it I took a close look at the grill and thought it looked odd and off center (upper left). It also looked small which led me to believe it may be a 158e.
The cancellation is Aug 15 and the enclosed letter(invoice) has a date of Aug 15(or close),1873.
There is a second grill at the lower left.
In reading on this forum there are not many cancelled 158e's. What does everyone think?

I am no expert but I think it looks like 136A with a split grill. I count the vertical rows at 10 and the horizontal at 13 for an I grill.
I await the experts to explain how I did.

158e used is a rarity. In addition to above grill notes, in the photo, the bottom ribbon shading looks just light enough to make it a 136.

Good point on the secret mark - it's not there. I think you were right at first. 136 or 136a - I'd want to see a rear view of the grill to determine which.

A good visual here.


https://goscf.com/t/38934&SearchTerms=136