Have taken on Issurer MM's myself and crunched and exchanged spreadsheets on more than one occasion ...
Issuer's (and hence MM's) work the THETA (time decay) which has more than one formula out there in formulae land.
Issuer's computations can be up to several times THETA on any given day as part of strategy to reduce the value of all Warrants to zero as quickly as possible ... hence their profit.
Your example of SG is typical of MM manipulation and occurs with all Issuer's over time you will find.
This practice shows itself with negative variations in IMPLIED VOLATILITY ... every trader should have a Option Pricing Model that solves for I/Vol so as to be able to detect these manipulations ...
Favourable movements in a stock towards Expiry generally results in an UPWARD movement in I/Volatility ... not DOWN !!!
Issuer MM's are required by the ASX to have a 'presence' at all times in the Market and do ... this can be viewed on Brokers screens and their antics can be monitored accordingly ...
Often it will be seen that this manipulation occurs when a stock moves suddenly so as to void an increase in value ... this kills the Taker's profit potential and makes a mockery of Warrants in general.
Bullsh*t explanations such as you describe are common place and are indicative of the cynical arrogance that is par for the course when dealing with Issuer's.
The Warrants Market is accordingly dying a rapid death and most traders are moving to ETO's and learning to trade the real thing ... a real Derivative Market that is ...
Where this occurs the first thing traders notice is PROFIT when they call it right ...
Others are exploring CFD's such as D4F with success.
