Using IR thermometer for measuring component temperature
What other factors need to be considered- is it the mass / profile / surface
  finish of various components, etc.. 


Only surface finish and material as that's what's emitting the IR.



Some reading:


  Most high-quality electrical tape has an emissivity of 0.95. One must be careful, especially with mid wavelength cameras (3-5 μm), that the tape is opaque. Some vinyl tapes are thin enough to have some infrared transmittance, and are therefore unacceptable for use as high-emissivity coatings. Scotch™ Brand 88 black vinyl electrical tape has an emissivity of 0.96 in both the short wavelength (3-5 μm) and long wavelength (8-12 μm) regions, and is recommended.  Source: FLIR.





  If you are using a thermometer with a fixed, preset emissivity of 0.95, and need to measure a shiny object you can compensate by covering the surface to be measured with spray oil, flat black paint or masking tape. Measure the temperature of the taped or painted surface. That is the true temperature. Source: Raytek.





  For relatively low temperatures (up to 500°F), a piece of masking tape, with an emissivity of 0.95, can be measured. Then adjust the emissivity value to force the indicator to display the correct temperature of the material. Source: Omega.




Each of the above articles is probably worth a read.