When mating a tender to a locomotive, you have to make the tender deck slightly lower than the cab floor to get the gangway plate to sit correctly. If the tender is too high the plate will rise upward at the coal pile end, coal will get under the edge and the fireman will have a difficult time doing his job. One also has to make note of the rear coupler height when picking up the rear of a tender to lower the front.
It is easier to shim the bolsters than to raise/lower the locomotive.
Having the tender with its rear slightly higher than the front will do nothing when you are on a 4% grade and the front of you 25 foot long tender is a foot higher than the rear.