MySQL How to calculate checkpoint age?
Those sequence numbers are necessarily large, monotonically increasing, numbers.  They are not byte offsets into the log.  You may find the number in the log, of you have fun with hex dumps.  (I don't.)
That Percona blog, while good, is a decade old.  A large log no longer delays restart as much as it once did.
Consider this for judging whether to increase (or decrease) the log_file_size:
Minutes between InnoDB log rotations = Uptime / 60 * innodb_log_file_size / Innodb_os_log_written
60 minutes is a good target, but it is not a precise target.
Beginning with 5.6.8, this can be changed dynamically; be sure to also change my.cnf.
innodb_log_files_in_group traditionally has been 2.  I suggest you use 2 unless you are on a new version of MariaDB, where it is no longer needed.