Getting back to the assertion of the OP - 3 months of not meeting a monthly SPH goal in a 12 month period of time and 'you're out'...
If this is true, then for each monthly period of time in which SPH goal isn't met - 'performance improvement' will have to be issued (functionally equivalent to Warning Letters). That would be a new one, even for Express.
I tend to be a bit skeptical on this one (I think a senior manager is expelling a lot of hot air to put fear into his employees - what a great leader...). If this assertion of the OP was the case, Express would be exposing itself to a potential of a class action suit - something even Express is wary of.
Ever since doing away with the performance review (all due to losing wrongful termination fights), Express has flailed about for a method to place some control on its wage employees. With the old performance review, Express essentially had an implicit 'contract' with its hourlies; that if they wanted some form of a pay raise, they'd have to met a certain set of criteria (degree of control) in order to get that raise. Things like punctuality, attendance (no sick calls), scan compliance, safety evaluation, and even sales lead submissions at one time were all part of the performance review. That is all gone now.
Employees are using sick days as de facto personal days (increasing OT costs and causing service failures), employees don't 'sweat' being late once every couple of months or so, and they ditched getting sales leads (what ever happened to those cheap sunglasses they were going to offer you guys anyway...). The personal incentive for getting an increase in pay was taken away, so was the ability of Express to 'control' its employees.
If anyone in Express HR had an ounce of sense, they would've predicted this and came up with an alternative method of coming up with some form of compensation that is INDIVIDUALLY targeted and not across the board to all employees. But along with the ending of the performance review, came a decision to hand out jokes for pay increases and essentially freeze compensation levels to being slightly less than annual inflation. This is all the price a corporation must pay as a consequence of screwing over its employees.
Whether or not Express is actually going to hand out Performance Reminders for failure to meet monthly SPH goal remains to be seen. Until and unless a poster here states they PERSONALLY know someone who has received a Performance Reminder for failure to meet SPH, I'd be very cautious about assuming Express would actually follow through on this senior manager's threat (that is what I'm viewing it as, at this point).
Firing employees over an arbitrary productivity goal of stops per hour just begs of class action litigation. Express would be left trying to prove that its Swing Couriers could meet the SPH goal for a route while the assigned Courier is chronically unable to (damn difficult to do). This is the key reason why Express (to date) has used SPH as an implicit 'threat' to its Couriers, but never actually followed through on issuing any form of discipline for meeting that goal. The SPH statistic is more of a way for district level management to hold operations managers' feet to the fire (thus why ops managers let the fecal material flow down to the Couriers). If a station's managers cannot get their Couriers to meet the SPH goal, it is THEY who are looking at disciplinary action. The only real way they can take the heat off themselves is to run check rides on routes that are not meeting the report 'goal', then if they find the Courier is working with correct methods and not making any screw ups, have the goal adjusted accordingly.
With all the crap that is flowing down to the hourlies at this point, worrying about SPH (unless someone reports actual performance improvement being issued), is a waste of time. You've other things to worry about (like trying to find another career at this point).