HoAg mana reservation help

Hey all, I am working on a HoAg Juggernaut in SSF HC. Going great so far and I have reached 91 but am having trouble with reservation with my herald.

Because I am using saffells shield, I have high elemental resists and chance to spell block but the physical is starting to worry me at higher levels.

I can currently only run herald of agony and tempest shield, I can throw in vitality if I want.

I have not found a way to fit determination into my reservation yet and I very much want it, I think I could by crippling my build and running all through the passive tree but I don't want to do that. Even with the determination mastery and multiple aura passive circle I still can't run tempest/herald/determination.

I am somewhat new with some of these mechanics but feel I may be missing something obvious.

I am currently trying a few things to make it work, testing out replica alpha howl for my herald, testing out reservation cluster jewels but they are hard to come by on ssf. Maybe I can use determination with divine blessing or an essence worm? I'm not sure

Farming lab for helmet enchant would be hard to get a specific one and I haven't found synthesis rings yet.
Any suggestions would be great, I'm still a bit new so even small things I may have missed would be appreciated. Remember I am on SSF HC so it may be a bit harder to find some of these things, but I can target farm some things I don't mind grinding a bit, I very much want this build to work so I can be tanky enough I can learn a bit more about end game.

I also linked my account I believe so if you see any obvious improvements to my build, point it out, I'd love some advice. So far its slow but loving it, love to be able to tank and learn these new things.

-ps technically not ssf but its HC on xbox so same thing really.

https://www.pathofexile.com/account/xbox/view-profile/DirkSunseteyes/characters

Quick thought, maybe I should take off tempest shield and go the less elemental ailment duration route. Or at least get less shock duration on my rings then replacing tempest shield for determination. Though I don't know how easy that is to get or how hard it would be to balance. I would also lose some spell block

I mean you can use "The Coming Calamity"
And then Herald reservation will always be 45%. I believe this is best in slot armour if you want to put some auras.
This is not rare unique item so why not. Also +2 to Herald gem is big

these rings can help if you can get them