A "genuinely remorseful and apologetic" Nash did not dispute the severity or impact of the incident at the hearing on Wednesday night, but argued for a three-game suspension.
It means the midfielder will miss Hawthorn's games against West Coast, Richmond, Melbourne and Gold Coast.
Nash had been sent straight to the tribunal after collecting Miers with a high, swinging arm in the Cats' seven-point win on Easter Monday.
Miers was subbed out immediately and will miss at least Sunday's clash with Carlton at the MCG after entering the 12-day concussion protocols.
The incident was assessed as careless conduct, severe impact and high contact.Â
Hawthorn argued the incident only warranted a three-week suspension given Nash had pleaded guilty at the earliest available time.
The club also made clear Nash hadn't used his fist to create excessive force against Miers and that he possessed an "unblemished tribunal record" in the same vein as AFL great and fellow Irishman Jim Stynes.
But the tribunal maintained, after 40 minutes of deliberation, that Nash had acted with severe force and a significant degree of carelessness.
Tribunal chair Jeff Gleeson KC added Nash was aware of Miers, given he had his arm on the opposition player's back.
"We have some difficulty in understanding how Mr Nash got it so wrong here," Gleeson said.
"We accept that he was not intending to strike Miers to the head, but he should have known that a forceful swing of an arm at head height may well result in such a strike."
Nash had presented the tribunal a text message he sent to Miers in the days after the match.
"Firstly, I just want to check in on how you've pulled up today. Hopefully not too bad and can get back on track soon," the message said.
"I'm also reaching out to let you know that there really wasn't any malice to that hit.
"I tried to play the ball and I just got it badly wrong.
"Yes, I do try to play the game with a physical presence, but not in that spirit and just want you to know that.
"Again, very sorry for what's happened and all the circus around it."
The AFL argued Nash warranted a four-week ban because he had a duty of care to a "vulnerable" Miers, and that the contact was made to the Geelong player's head.
Miers looked to be concussed before he hit the ground and staggered off the field with the help of medical staff.
Parallels were drawn with Fremantle player Patrick Voss and Hawthorn teammate Jack Scrimshaw's respective three-match suspensions handed down earlier in the season.
But the AFL argued the cases were not similar, given there was no immediate concern of concussions to the victim players during the incidents.
Richmond player Nick Vlastuin suffered a broken nose after being struck by Voss, and Essendon defender Jordan Ridley played out the rest of the second quarter after his incident with Scrimshaw.
Ridley was eventually substituted out of the match at half-time with a concussion.
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