The six clubs will be allocated a pool each when the draw is made for the 2011-12 campaign at Twickenham next Tuesday and then joined by a team from each of the next three tiers.
The seeding system employed by tournament organisers European Rugby Cup is based on performances in the Heineken Cup and Amlin Challenge Cup over the past four years.
This year's beaten Heineken Cup finalists Northampton had the same ranking points as Leicester but were edged into the second tier because they missed out on the tournament in 2008-09.
One frustrating anomaly for the Saints is that their 2009 Challenge Cup victory was only worth five points, compared to the six earned by subsequent champions Cardiff and Harlequins.
ERC increased the ranking points available for winning the Challenge Cup when the competition was restructured to include teams dropping down from the Heineken Cup.
That one extra point would have earned Northampton a top seeding. Instead they are grouped with Clermont Auvergne, Ospreys, Bath, Harlequins and London Irish.
The prospects of another so-called group of death emerging from next week's draw are strong.
Aviva Premiership champions Saracens are in tier three while French Top 14 finalists Montpellier join Racing Metro and Heineken Cup debutants Connacht in tier four.
No pool will have more than one club from the same country, with the exception of England because seven Premiership teams qualified.
TIER 1 - Leinster, Toulouse, Munster, Cardiff Blues, Biarritz Olympique, Leicester Tigers
TIER 2 - Northampton Saints, ASM Clermont Auvergne, Ospreys, Bath Rugby, Harlequins, London Irish
TIER 3 - Ulster Rugby, Saracens, Gloucester Rugby, Glasgow Warriors, Scarlets, Edinburgh
TIER 4 - Connacht Rugby, Benetton Treviso, Castres Olympique, Montpellier, Racing Metro 92, Aironi Rugby
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