4-4-0 Steam Locomotives on PECO Unifrog Turnouts

[RBDNHM]

I have repeated issues with my Bachman 4-4-0 steamer locomotives (all three of them - W.A.R.R., 119, & 60) shorting in both directions at the frogs on my PECO unifrog #6 turnouts (both right and left). My layout also has electrofrog turnouts, which do not seem to have any of the same problems.  I do not have the same problems with any other locomotives, diesel or steam.

It looks as if the wheel tread/width of the larger drive wheels is wide enough to cross the small sliver of insulation between the two rails that meet at the frog, resulting in the short.  I have read discussions online about using nail polish or some insulating material on the top of the rails at the meeting point for perhaps 1/8-1/4" to prevent the short, and I have tried that. It seems to work about half the time.

Is there a modification of the 4-4-0 wheels or locomotive that may help to eliminate the short?

Thank you in advance for any help.

RBD