Some of the links on this forum allow SMF, at no cost to you, to earn a small commission when you click through and make a purchase. Let me know if you have any questions about this.
Yes, a dial thermo mounted on the side of a UDS will not give you an accurate temp at the center of the drum.
If I were you I would try to measure the temp at the center either with an oven thermo or a digital probe. After it is running awhile at your desired center temp, see what temp the dial thermo on the side says then use that as your reference point when using the dial thermo.