Sounds about right... if you find that the tack loads are difficult to manage direct, you could add a 2 part tackle on the front end... give you more oomph but you'll be pulling more line. On 28 feet you'll probably be fine, and if necessarry you can luff the sail to adjust the tack (or use a winch that may already be behind the stopper)
Enjoy the sail... it'll make a big difference on those light reachy days, and give you some thrills when it's windier.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)