Yes, that´s right. From -8dB on up there is very ltttle difference in the required value of the swamping resistor. I think 9 Ohms would be a good average size from -8dB upwards.Since the crossover is designed for an 8ohm driver, you will want to use a 'swamping' resistor across the primaries of your autoformer that 'present' an ~8ohm impedance to your crossover.
Based on intact audio and the calculator there, for an 8ohm driver, 8ohm crossover impedance, and ~12dB of attenuation you would need an ~8.5ohm 'swamping' resistor across the primaries of the autoformer.
I think that's right, and hope others will chime to confirm. FWIW, it's the plan I'm working on implementing on my crossovers in the next week or so. The difference for me is I'm using Werner Jagusch's (sp?) autoformers.