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

for _ in range(int(input())):
    n=int(input())
    l=list(map(int,input().split()))
    x=sorted(l)
    if x[0]==x[-1]:
        print(-1)
    else:
        a=x[-1]
        f=0
        for i in range(n-1):
            if l[i]==a and l[i+1]<a:
                print(i+1)
                f=1
                break
        if f==0:
            for i in range(1,n):
                if l[i]==a and l[i-1]<a:
                    print(i+1)
                    f=1
                    break
        if f==0:
            print(-1)
                    
        
