1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

# cook your dish here
#import sys
#input=sys.stdin.readline
#m=int(input())
for nt in range(int(input())):
    n=int(input())
    lst=list(map(int,input().split()))
    k=max(lst)
    if len(set(lst))==1:
        print(-1)
    else:
        for i in range(0,n):
            if i>=1 and lst[i-1]<k and lst[i]==k or i<=n-2 and lst[i+1]<k and lst[i]==k:
                r=i+1
                break
        print(r)
        
    