Hey Andy,
I just had a look at Optidrive E3 Advanced Technical Manual Issue 2003 and E3 IP66 Outdoor User Guide V1.23 NEW but I just found
Suitable resistors and guidance on selection can be obtained from your Invertek Sales Partner.
That helps! 
I found my brake resistor by choosing it under “Accessories” in my Omron MX2 Users Manual:
Mine has 70 Ω/0.2 kW. My VFD and Spindle are 2.2 kW 220 V too (my VFD Model is 3G3MX2-AB022-E)