Verb form συνησθησομένους in letter of Julian

I have a nagging query about the verb form συνησθησομένους in epistle 54 of Julian in the Cambridge green and yellow “Greek and Latin Letters” anthology ed M Trapp p84. The context is about calling your neighbours to your feast ως συνησθησομένους i e they share our grief in hard times. My question is shouldn’t the future participle be συναισθησομένους, or am I missing something obvious? Any clarification would be greatly appreciated.

-η- instead of -αι- means it must be from συνήδομαι rather than συναισθάνομαι. Does that make more sense?

Thank you so much Phalakros. That’s definitely it. I’d been understanding it as that the neighbours shared our grief in hard times, whereas it’s that because they share our grief in hard times they also rejoice with us in good times. Thank you again for your help with that.