Roger, the thickness of the decal film stock makes the difference there. Even using something stronger: There's the Microscale fluid in the red print bottle, or Walther's Solvaset won't help.
I know there are other companies that make plain decal stock, but the newer Microscale stuff is very thin.
On a project like yours, I might have taken a different approach. On steam tenders like yours, I'll design and make it on my computer, then print it out on a gloss stock 34lb. paper... same concept as yours: White, gold or yellow lettering on a black background. But I'll cut the paper the full length as the tender body.
You have to use a black marker on the edge of the paper. Yes, you do see the line, but it looks a little more orderly being a straight line across the entire tender length, versus the "blob" sort of shape left by the decal film. I've also placed a white, gold or yellow line above and below the lettering, and then cut along those lines, which really does a better job at "hiding" the cut line.
But I wouldn't worry about it too much. Given the before and after, the engine and tender look so much better now.
