Exactly what do you mean by a "firmware reset?" Did you actually re-flash the firmware on your board? If so, what was the reason for doing so?
I'm not quite sure I understand the problem. But there are three numbers that the 'bot uses for each axis:
1) Steps per millimeter
. This is the "scale" and determines how big your print will be. For several years now, Printrbots have been shipped with GT2 belts, which have 80 steps per mm on the X and Y axes. If you have a really old Plus and you've never replaced the belts and pulleys, then your steps/mm may be different. The steps per mm on the Z axis depends on the type of screw used to actuate Z. In all cases, (X, Y, Z; new or old) you should use the steps per mm that are calculated from the hardware you are using. The steps per mm are in EEPROM, stored in the M92 parameters. You read out the EEPROM with M503 command; you can make changes with M92, and then store back into EEPROM with M500. See viewtopic.php?f=18&t=2763
2) Location of origin
. Consumer-grade 3D printers never have sensors that tell the printer where the printhead is actually located. They work by doing a "home" command first, and then keeping track of the steps moved away from home. Every time you power down the printer, the information about "home" is lost, so every time you turn it on it's necessary to do a "homing" sequence. Most slicers, by default, incorporate this homing sequence into the beginning of the G-code for printing a part. But you also can do it yourself, using the little "home" icons on the User Interface screen (that's how I do it).
3) Limits of travel
. This is essentially the bed size in X and Y, and the available height in Z. Every version of firmware available has pre-defined default limits set up internally. Unfortunately, not every version of Marlin has available EEPROM settings that would allow you to change those limits. When you do an M503, look for a line in the resulting log file that says it's defining the limits of travel. This will probably be called Max Position and probably be defined as M211. If you have this available in your EEPROM, you can change the numbers. If your version of Marlin doesn't have it available in EEPROM, and you are sure that your limits of travel are wrong, then you'll have to flash a different version of Marlin that either does have the right limits or allows you to change them.