Looks good. This is one for Creedo's site. I've tabulated all the mobiles here, have a look:

.............. | ..Full Power.. | 2 Bars
..Mobile.. | (Full-screen). | (Half-Screen)
========================
nak......... | 77.00 | 59.37
trico........ | 77.90 | 62.47
raon........ | 79.00 | 65.74
asate...... | 79.00 | 65.74
armor...... | 79.50 | 67.11
turtle....... | 79.50 | 67.11
mage....... | 80.00 | 68.42
lightning.. | 80.50 | 69.69
aduka...... | 80.70 | 70.18
ice........... | 81.10 | 71.15
boomer... | 81.20 | 71.39
JD............ | 81.20 | 71.39
grub........ | 81.70 | 72.58

The originally posted formula is correct. There was no need for a correction.

Round off the angles as you see fit. (And no I did not calculate each mobile, I used Excel spreadsheet to calculate once, and copied the formula down the line...)

I've been using 72 2-bar for boomer to reach half-screen, so it's very close.

Once you calculate all the above, you'll never use this formula again, much less in the game!